Fault tolerant turbine speed control system

ABSTRACT

A generator is installed on and provides electrical power from a turbine by converting the turbine&#39;s mechanical energy to electricity. The generated electrical power is used to power controls of the turbine so that the turbine can remain in use through its own energy. The turbine can be a safety-related turbine in a nuclear power plant, such that, through the generator, loss of plant power will not result in loss of use of the turbine and safety-related functions powered by the same. Appropriate circuitry and electrical connections condition the generator to work in tandem with any other power sources present, while providing electrical power with properties required to safely power the controls.

BACKGROUND

FIG. 1 is a schematic diagram of a conventional turbine control systemin commercial nuclear power stations. As shown in FIG. 1, a turbine 100receives source steam 101, extracts thermodynamic energy from the sourcesteam 101, and outputs lower-pressure, saturated steam 102. Source steam101 may be from a nuclear reactor, a heat exchanger, a steam generator,a higher-pressure turbine etc. Turbine 101 may be any turbine found innuclear power plants, including a lower-output Reactor Core IsolationCooling (RCIC) turbine or higher-output High Pressure Injection Cooling(HPIC) turbine, for example. The extracted energy 105 is used to powerdesired components; for example, in the case of an RCIC and HPIC,extracted energy 105 provides power to associated RCIC and HPIC coolingpumps that maintain flow and water levels in a reactor.

When a turbine 100 is used to run cooling systems to maintain reactorcoolant levels and remove decay heat from the plant, such as in atransient scenario, turbine 100 is controlled by a speed controller 60.Turbine 100 generates speed information based on load and output andtransmits speed information signals 61 to speed controller 60. Speedcontroller 60 generates speed control signals 62 based on received speedinformation signals 61 to be transmitted back to turbine 100. Speedinformation signals 61 permit turbine 100 to operate at specified speedsand loads to avoid tripping and provide adequate power 105 to desireddestinations. Speed controller 60 is conventionally networked with aflow controller 55 in the plant control room, which exchanges flowcontrol signals 56 with the speed controller 60. In this way, plantoperators may monitor and input speed commands through the control roomflow controller 55 that are translated into speed control signals 62 byspeed controller 60 and ultimately control turbine 100 to perform inaccordance with control room commands.

Control room flow controller 55 and speed controller 60, and data andsignals generated thereby, are conventionally powered by offsite orplant power. As shown in FIG. 1, when such power is unavailable, such asduring a station blackout event, a plant emergency power distributionsource 50, such as a local diesel generator or battery, may provideelectrical output 51 to control room flow controller 55 and speedcontroller 60. By offering local power, emergency power distributionsource 50 may permit operators to continuously control a speed of anduse turbine 100 to manage the transient and/or provide power to safetysystems, including Core Isolation and High Pressure Injection Coolingpumps.

SUMMARY

Example embodiments include methods and systems for controlling turbinespeed using the turbine's own power such that offsite power or localemergency power are not required to operate the turbine. Example systemsinclude a generator connected to the turbine and generating powertherefrom and connected to a controller for the turbine, such as a speedcontroller or control room flow controller governing turbine behavior.The generator may be of any appropriate power, voltage, frequency, etc.to power the controller and any other desired system. Exampleembodiments may further include circuitry connecting the generator,controller, and plant emergency power with isolation diodes between eachpower source and a filter to provide electrical power having propertiesrequired to power the controller.

By installing and using a generator on a turbine in a nuclear powerplant to power turbine controllers, the turbine may be operated andcontrolled through its own power without concern for offsite or localpower. If the turbine drives safety-related pumps like RCIC or HPIC, atleast the turbine may be operated and controlled through exampleembodiments and methods by plant operators to provide emergency coolingto a reactor that has lost offsite and onsite emergency power, as longas the turbine can be driven by decay heat or other steam sources. Thismay greatly extend core cooling capacity in some accident scenarioswhile eliminating any need for manual intervention to operatesafety-related turbines.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Example embodiments will become more apparent by describing, in detail,the attached drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusdo not limit the terms which they depict.

FIG. 1 is a schematic diagram of a conventional commercial nuclearreactor turbine flow control system.

FIG. 2 is a schematic diagram of an example embodiment fault tolerantturbine speed control system.

DETAILED DESCRIPTION

This is a patent document, and general broad rules of constructionshould be applied when reading and understanding it. Everythingdescribed and shown in this document is an example of subject matterfalling within the scope of the appended claims. Any specific structuraland functional details disclosed herein are merely for purposes ofdescribing how to make and use example embodiments. Several differentembodiments not specifically disclosed herein fall within the claimscope; as such, the claims may be embodied in many alternate forms andshould not be construed as limited to only example embodiments set forthherein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected,” “coupled,” “mated,” “attached,” or “fixed” to anotherelement, it can be directly connected or coupled to the other element orintervening elements may be present. In contrast, when an element isreferred to as being “directly connected” or “directly coupled” toanother element, there are no intervening elements present. Other wordsused to describe the relationship between elements should be interpretedin a like fashion (e.g., “between” versus “directly between”, “adjacent”versus “directly adjacent”, etc.). Similarly, a term such as“communicatively connected” includes all variations of informationexchange routes between two devices, including intermediary devices,networks, etc., connected wirelessly or not.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude both the singular and plural forms, unless the languageexplicitly indicates otherwise with words like “only,” “single,” and/or“one.” It will be further understood that the terms “comprises”,“comprising,”, “includes” and/or “including”, when used herein, specifythe presence of stated features, steps, operations, elements, ideas,and/or components, but do not themselves preclude the presence oraddition of one or more other features, steps, operations, elements,components, ideas, and/or groups thereof.

It should also be noted that the structures and operations discussedbelow may occur out of the order described and/or noted in the figures.For example, two operations and/or figures shown in succession may infact be executed concurrently or may sometimes be executed in thereverse order, depending upon the functionality/acts involved.Similarly, individual operations within example methods described belowmay be executed repetitively, individually or sequentially, so as toprovide looping or other series of operations aside from the singleoperations described below. It should be presumed that any embodimenthaving features and functionality described below, in any workablecombination, falls within the scope of example embodiments.

Applicants have recognized plant emergency power distribution system 50may become unavailable during plant transients. Indeed, it may bepossible that the same transient event that cuts offsite power mayrender unusable emergency power distribution system 50. In such asituation, turbine 100 may not be monitored, controlled, or potentiallyeven used by plant operators in the control room to provide power output105 to emergency systems or otherwise, because turbine speed controller60 and/or control room flow controller 55 lack emergency power.Applicants have further recognized that turbine 100 itself may provideemergency electrical output if all other offsite and onsite power arelost, and that such power, if properly diverted, may be used to powerspeed controller 60 and control room flow controller 55, such thatoperators may use turbine 100 to manage a plant transient even in theevent of loss of all other power. Example embodiments and methodsdiscussed below enable these and other advantages and solutions tosituations appreciated by Applicants.

FIG. 2 is a schematic drawing of an example embodiment fault tolerantturbine speed control system 1000. As shown in FIG. 2, an electricalgenerator 500 is installed on turbine 100 and electrically connected tospeed controller 60 and control room flow controller 55. Generator 500may be any type of generator, including AC or DC power generators,capable of generating voltage from mechanical energy 515 of turbine 100.Generator 500 may be installed along a turbine shaft of turbine 100 andgenerate electrical power 551 from mechanical energy 515 output on theshaft. Existing mechanical output 105 may still be produced by turbine100 in example embodiments.

Generator 500 may be capable of delivering any amount of electricalpower 551 that is sufficient to power connected systems, such as speedcontroller 60 and/or control room flow controller 55. For example,generator 500 may be a 200 W DC generator that can power both speedcontroller 60 and control room flow controller 55 conventionallyinstalled in nuclear power plants. Of course, generator 500 may have amuch larger or smaller wattage, depending on need and mechanical poweroutput of turbine 100. If functionality of turbine 100 is desired forother components, such as coolant pumps powered by turbine output 105,generator 500 may be rated at an electric power less than a differencebetween turbine 100's capacity and required output 105. For example, a 1kW DC generator may power additional systems while not interfering withoperations of a larger turbine 100.

As shown in FIG. 2, generator 500 is electrically connected to turbinecontrollers, such that if electrical output 51 from emergency powerdistribution system 50 becomes unreliable or unavailable (as indicatedby “X” in FIG. 2), electrical power 551 from generator 500 maysupplement or replace electrical output 51 from emergency systems.Generator 500 may be electrically connected to a plant power network andthus electrically power plant components by installing an electricalconnection or circuit between generator 500 and the network.

Isolation diodes 505 and/or filter 501 may be installed or configured asdesired to provide effective electrical current, voltage, power,frequency, timing, etc. to all components connected to the network.Isolation diodes 505 and/or filter 501 may ensure that such electricalpower supplementing or replacing power from emergency power distributionsystem 50 matches voltage and power characteristics required to safelyrun emergency systems like generator 500, speed controller 60, controlroom flow controller 55, and/or any other plant component that can bepowered by electricity from generator 500. Isolation diodes 505 may alsoensure that power from generator 500 can reach consuming components onthe electrical network regardless of malfunction or complete loss ofemergency power distribution system 50. For example, isolation diodes505 may prevent or reduce reverse current surges to generator 500 and/oremergency power distribution system 50 so as to prevent damage orineffectiveness in those components. Filter 501, which may be acapacitor or battery, for example, may be grounded and smooth currentand voltages applied to speed controller 60, control room flowcontroller 55, and any other component being powered by generator 500.

Alternatively, generator 500 may be directly electrically connected todesired components such as speed controller 60 and/or control room flowcontroller 55 so that those components may themselves switch togenerator 500 electrical power 551 in the instance of failure of plantemergency power distribution system 50.

As shown in FIG. 2, when speed controller 60 and/or control room flowcontroller 55 are powered by turbine 100 through generator 500, plantoperators may continuously operate turbine 100 by monitoring andcontrolling the speed of the same from the control room via signals 61,62, and/or 56. In this way, turbine 100, and its output 105, may be usedeven with a total failure of plant emergency power distribution system50. If turbine 100 is an RCIC, HPIC, or other transient- orsafety-related turbine, mechanical power output 105 may be maintained toemergency systems, such as an RCIC or HPIC pump, through example systemsusing generator 500. As long as a steam source 101 is available, such asfrom decay heat from a reactor or other source, turbine 100 may operateand be controllable in example systems, regardless of complete loss ofstation power and emergency electrical backups. As such, example system1000 may permit prolonged use and control of turbine 100 to power otheremergency systems that preserve reactor or plant integrity during atransient event.

Example embodiments and methods thus being described, it will beappreciated by one skilled in the art that example embodiments may bevaried and substituted through routine experimentation while stillfalling within the scope of the following claims. For example, althoughexample embodiments are described in connection with RCIC or HPICturbines in nuclear power plants, it is understood that exampleembodiments and methods can be used in connection with any turbine whereloss of power affects the ability to control and/or use the turbine.Such variations are not to be regarded as departure from the scope ofthe following claims.

What is claimed is:
 1. A nuclear plant emergency power system comprising: a turbine configured to power a coolant pump for a nuclear reactor; a speed controller configured to monitor a speed of the turbine and control a speed of the turbine; a control room flow controller configured to receive turbine information from the speed controller and transmit turbine speed commands to the speed controller; an emergency power distribution system electrically connected to the speed controller and the control room flow controller; and a generator electrically connected to the speed controller and the control room flow controller, wherein the generator is a maximum 200 Watt electric generator, wherein the generator is configured to generate electrical power from the turbine and provide the electrical power to the speed controller and the control room flow controller.
 2. The system of claim 1, wherein the speed controller and the control room flow controller are remote from the turbine.
 3. The system of claim 1, wherein the generator is a DC generator.
 4. The system of claim 1, wherein the emergency power distribution system includes at least one isolation diode and filter to condition the electrical power provided to the speed controller and/or control room flow controller.
 5. The system of claim 4, wherein the isolation diode prevents current surges to the generator and wherein the filter is a capacitor configured to reduce voltage surges.
 6. The system of claim 1, wherein the speed controller and/or control room flow controller are configured so that the operation of the speed controller and/or control room flow controller with the electrical power permit the turbine to be controlled regardless of input from the emergency power distribution system.
 7. The system of claim 1, wherein the generator is configured to immediately power the speed controller and the control room flow controller following a loss of offsite power.
 8. The system of claim 1, wherein the generator is of a power less than an electric equivalent of a difference between a maximum mechanical output of the turbine and a mechanical power required to operate the coolant pump.
 9. The system of claim 1, further comprising: circuitry configured to electrically connect the generator and the speed controller, and connect the generator and the control room flow controller.
 10. The system of claim 9, wherein the circuitry connects all of the emergency power distribution system, the generator, the speed controller, and the control room flow controller.
 11. The system of claim 10, wherein the circuitry includes, isolation diodes configured to prevent current flow to the generator and to the emergency power distribution system, and a filter configured to reduce voltage surges in the circuitry.
 12. The system of claim 1, wherein the generator is directly electrically connected to the speed controller without interruption by any electrically-powered device.
 13. The system of claim 1, wherein the turbine is configured to convert energy from a coolant flowing from the reactor to the turbine to power the coolant pump.
 14. The system of claim 1, wherein the turbine is configured to directly connect to the coolant pump and directly transfer mechanical energy to the coolant pump.
 15. The system of claim 14, wherein the turbine is an RCIC turbine configured to convert energy from a coolant flowing from the reactor to the RCIC turbine to directly power the coolant pump.
 16. The system of claim 1, wherein the speed controller is configured to adjust the speed of the turbine when in operation in accordance with the speed commands.
 17. The system of claim 1, further comprising: a capacitor electrically connected to the generator, the control room flow controller, and the speed controller.
 18. The system of claim 1, wherein the control room flow controller and the speed controller are separate from each other and remote from the turbine.
 19. The system of claim 1, wherein the turbine is configured to generate mechanical power from decay heat from a coolant in the nuclear reactor, and wherein the generator is configured to convert the mechanical power to electricity to control the speed of the turbine.
 20. The system of claim 1, wherein the emergency power distribution system includes a battery, and wherein the generator is configured to provide the electrical power to only the speed controller and the control room flow controller. 